Amplitude-modulated Waveforms Research Articles

Dual-wavelength sub-Nyquist sampling scheme for clipping-avoidance photonic ADC

We propose a dual-wavelength scheme for a clipping-avoidance photonic analog-to-digital converter (PADC) operating at the sub-Nyquist sampling rate. The scheme utilizes two characteristics, the phase-wrapping feature of a PADC and the wavelength-sensitive feature of a phase modulator, equivalently performing a dual-modulus (DM) modulo operation to avoid clipping. Coupled with an unwrapping algorithm based on the Chinese remainder theorem (CRT), the proposed scheme enables signal reconstruction from the processed signals independent of the sampling rate. We demonstrated proof-of-concept experiments on a PADC chip fabricated on an LNOI platform. Experimental results show that 1G/2G/4G-baud 10-level pulse amplitude modulation (PAM-10) waveforms were successfully reconstructed at the sub-Nyquist sampling rate of 1/2/4Gs/s, respectively. Our work provides a potential solution to achieve on-chip clipping-avoidance PADCs operating at the sub-Nyquist sampling.

Unambiguous acquisition algorithm based on sub‐correlation functions combination for semi‐integer CPM signals

AbstractDue to the nonlinear nature of continuous phase modulation (CPM), most existing unambiguous acquisition algorithms are ineffective in eliminating the ambiguity threat faced by semi‐integer CPM signals. To address this issue, this letter proposes an unambiguous acquisition algorithm based on sub‐correlation functions combination (SCFC). The main idea of this algorithm is to decompose the first pulse amplitude modulation waveform derived from the Laurent decomposition into sub‐signal waveforms that are appropriate for CPM signals. The final unambiguous function is obtained by combining the autocorrelation function of the received CPM signal with the sub‐correlation functions derived from the sub‐signal waveforms and the received CPM signal. Simulation results demonstrate that the SCFC algorithm can eliminate the ambiguity threat of semi‐integer CPM signals with relatively minor detection loss. Moreover, the proposed algorithm successfully retains a narrow main peak and exhibits superior multipath resistance.

Temporal interference stimulation disrupts spike timing in the primate brain

Electrical stimulation can regulate brain activity, producing clear clinical benefits, but focal and effective neuromodulation often requires surgically implanted electrodes. Recent studies argue that temporal interference (TI) stimulation may provide similar outcomes non-invasively. During TI, scalp electrodes generate multiple electrical fields in the brain, modulating neural activity only at their intersection. Despite considerable enthusiasm for this approach, little empirical evidence demonstrates its effectiveness, especially under conditions suitable for human use. Here, using single-neuron recordings in non-human primates, we establish that TI reliably alters the timing, but not the rate, of spiking activity. However, we show that TI requires strategies—high carrier frequencies, multiple electrodes, and amplitude-modulated waveforms—that also limit its effectiveness. Combined, these factors make TI 80 % weaker than other forms of non-invasive brain stimulation. Although unlikely to cause widespread neuronal entrainment, TI may be ideal for disrupting pathological oscillatory activity, a hallmark of many neurological disorders.

A Single-Board Integrated Millimeter-Wave Asymmetric Full-Digital Beamforming Array for B5G/6G Applications

In this article, a single-board integrated millimeter-wave (mm-Wave) asymmetric full-digital beamforming (AFDBF) array is developed for beyond-fifth-generation (B5G) and sixth-generation (6G) communications. The proposed integrated array effectively addresses the challenge of arranging a large number of ports in a full-digital array by designing vertical connections in a three-dimensional space and successfully integrating full-digital transmitting (Tx) and receiving (Rx) arrays independently in a single board. Unlike the traditional symmetric array, the proposed asymmetric array is composed of an 8 × 8 Tx array arranged in a square shape and an 8 + 8 Rx array arranged in an L shape. The center-to-center distance between two adjacent elements is 0.54λ0 for both the Tx and Rx arrays, where λ0 is the free-space wavelength at 27 GHz. The proposed AFDBF array possesses a more compact structure and lower system hardware cost and power consumption compared with conventional brick-type full-digital arrays. In addition, the energy efficiency of the proposed AFDBF array outperforms that of a hybrid beamforming array. The measurement results indicate that the operating frequency band of the proposed array is 24.25–29.50 GHz. An eight-element linear array within the Tx array can achieve a scanning angle ranging from −47° to +47° in both the azimuth and the elevation planes, and the measured scanning range of each eight-element Rx array is –45° to +45°. The measured maximum effective isotropic radiated power (EIRP) of the eight-element Tx array is 43.2 dBm at 28.0 GHz (considering the saturation point). Furthermore, the measured error vector magnitude (EVM) is less than 3% when 64-quadrature amplitude modulation (QAM) waveforms are used.

Incorporating the Time-synchronous Averaging Method into Vibration Analysis Methodologies for the Detection and Localization of Bearing Defects

Objective: The objectives of this paper are to highlight the significance of vibration analysis, especially in predictive maintenance for rotating machinery, and to emphasize the importance of detecting bearing defects that may result in machinery failure. Methods: The proposed methodology combines the use of time-synchronous averaging (TSA) with existing vibration analysis techniques. TSA involves aligning vibration data with specific events or phases in the machinery's operation, such as shaft rotation. By synchronizing the data in this way, the methodology aims to reduce noise and enhance the signal related to bearing defects, making them more distinguishable. Additionally, the methodology incorporates well-established vibration analysis techniques. These techniques may include frequency analysis, amplitude modulation analysis, waveform analysis, and others commonly used in the field of condition monitoring and predictive maintenance. Results: The results of the analysis begin with waveform analysis, which involves examining the shape and pattern of vibration signals captured from the pinion. This analysis provides valuable insights into the dynamic behavior of the pinion gear, including any variations or abnormalities in its motion. Moreover, the use of synchronized waveforms is crucial in this analysis. By aligning the vibration data with specific events or phases in the gear mesh cycle, such as tooth engagement, the analysis can pinpoint moments when potential faults or wear in the machinery may occur. This synchronization allows for a more precise assessment of the vibration signals, enabling the detection of irregularities that may indicate underlying issues with the pinion or other components of the machinery. Conclusion: A pivotal aspect of the methodology involves envelope spectra analysis, significantly enhancing diagnostic capabilities. This analysis identifies fault patterns that might not be readily apparent in conventional vibration analysis. The incorporation of envelope spectra proves instrumental in proactive maintenance, enabling early detection of potential issues. This, in turn, contributes to the overall reliability and optimization of machinery performance.

Effects of ‘step-like’ amplitude-modulation on a pulsed capacitively coupled RF discharge: an experimental investigation

We present measurements of the time evolution of plasma and electrical parameters in a pulsed capacitively coupled argon discharge operated at a radio frequency of 12.5 MHz, whose amplitude is ‘step-up’ and ‘step-down’ modulated. The ‘step-up (-down)’ amplitude-modulated waveform consists of three segments, i.e., a low (high)-voltage, a high (low)-voltage, and a zero-voltage stage. Here, we focus on the effect of the ratio (ζ = V L/V H ⩽ 1) of the low-(V L) to high-voltage (V H) amplitude (measured at the end of the respective segment) on the time evolution of discharge parameters. We monitor the behavior of the discharge by measuring (i) the optical emission intensity (OEI) of a selected Ar-I spectral line, (ii) the electron density at the center of the plasma (using a hairpin probe) as well as (iii) the electrical characteristics (by voltage and current probes). It is found that at relatively large ζ (i.e., at low disparity between the two voltage amplitudes), for both the ‘step-up’ and ‘step-down’ cases, these parameters evolve relatively smoothly with time upon changing the voltage amplitude, and the ignition process strongly depends on the duration of the zero-voltage period. At low ζ (i.e., at high disparity between the voltage amplitudes), an abnormal evolution of the parameters can be observed during the low-voltage period for both cases. Specifically, the voltage amplitude and the modulus of the system impedance increase to a higher value, while the relative phase, φ vi, between the voltage and the current approaches 90°, resulting in a reduction of the power deposition and the OEI. The enhanced voltage amplitude decreases to a steady-state value, accompanied by a decline of φ vi, and an abnormal increase of the current amplitude and the electron density after some time, of which the duration increases with the decrease of ζ. The ζ-dependent evolution of the electron density during the low-voltage period was found to significantly affect the subsequent ignition process and electron power absorption mode at the beginning of the high-voltage period.

Dual-Beam Steerable TMAs Combining AM and PM Switched Time-Modulation.

Wireless sensor networks (WSN) are increasingly requiring directional antennas that not only provide higher capacity, security, transmission range or robustness against interference, but also contribute with smart antenna capabilities such as adaptive beamforming or multi beam radiation patterns. Standard phased arrays provide these features, but employing feeding networks based on digitally controlled variable phase shifters (VPSs) which have the disadvantage of high cost and limited angular resolution. Instead, time-modulated arrays (TMAs) use switched feeding networks governed by digital periodic sequences which allow harmonic patterns to be radiated and endows (TMAs) with attractive multifunctional capabilities. In this paper, we analyze and properly combine (TMA) switched feeding networks capable of time-modulating an antenna array with discretized amplitude modulation (AM) and phase modulation (PM) waveforms. The advantages of the proposed innovative dual-beam (TMA) with respect to the competing architectures are, on the one hand, its power efficiency and beamsteering (BS) phase sensitivity and, on the other, its hardware simplicity, which allows for an excellent relative cost advantage.

Maximal‐ratio combining detection in massive multiple‐input multiple‐output systems with accurate probability distribution function

This letter derives the probability distribution function (PDF) of received symbols for orthogonal frequency-division multiplexing (OFDM) based massive multiple-input, multiple-output (MMIMO) systems, which uses maximal-ratio combining (MRC) detection. The effects of noise and interferences are evaluated through random variables, and the PDF is then derived from their joint probability and characteristic functions. The bit error rate (BER) using Binary and Quadrature Phase Shift Keying (BPSK, QPSK), and M-ary Quadrature Amplitude Modulation (QAM) waveforms is then analyzed by using this PDF. Simulation and analytical results confirm that the derived equations provided accurate PDF and BER, and therefore, can be used efficiently to evaluate performance of OFDM-MMIMO systems.

A High Spatiotemporal Resolution Ultrasonic Ranging Technique With Multiplexing Capability

In this article, a high-performance water-coupled ultrasonic ranging technique is presented. We improved the conventional time-of-flight (ToF) ranging technique based on digital correlation of pseudorandom noise (PRN) waveforms by introducing signal carrier phase shift detection with an I/Q coherent reception method. In this way, the spatial resolution is dominated mainly by the digitization resolution of the analog-to-digital converter (ADC) used in the receiver circuit. Submicrometer resolution is achieved in the entire full-scale-range (FSR) while keeping the ADC sampling rate at the Nyquist sampling limit of the carrier frequency of ranging signal. In this study, we use quadrature amplitude modulation (QAM) waveforms of a set of 1023-bit GPS Gold codes with 8 MHz carrier as a ranging signal. Experiments carried out in a water vessel reveal micrometer-level accuracy and precision for quasi-static and dynamic cases. It is experimentally illustrated that the proposed method is capable of multiplexing. The optimal ranging performance is approached by selecting an appropriate set of systemic technical parameters and ranging signals. This allows to define the figure of merit (FOM) indicating the performance upper bound of such a ranging system.

Adaptive filter bank multi-carrier waveform design for joint communication-radar system

We present a transmit power adaptive filter-bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) waveform for joint communication and radar system. For frequency selective fading channels or frequency sensitive targets, a joint optimization problem is designed by taking both the radar detection performance and communication channel capacity into the objective function under the constraint of limited transmit power. In addition, we derive the power allocation condition where the optimal performance of radar and communication can be achieved simultaneously. Otherwise, the tradeoff between radar and communication performance is necessary by adjusting the weighting factor. The proposed algorithm can realize adaptive transmission where the parameters of the transmitting waveform can be optimally designed for the next pulse by utilizing the measured values of the current signal and the channel state information. Moreover, the feasibility and advantages of FBMC as the radar signal are analyzed from the aspects of average ambiguity function, multipath effect and Doppler shift. Simulation results verify the effectiveness of the proposed scheme. Compared with the equal power allocation, the proposed adaptive transmission power algorithm in this paper shows better performance.

Temporal interference stimulation targets deep brain regions by modulating neural oscillations

BackgroundTemporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range with the goal of non-invasive targeted deep brain stimulation. Yet, the current intensities required in human (sensitivity) to modulate deep brain activity and if superficial brain region are spared (selectivity) at these intensities remains unclear. ObjectiveWe developed an experimentally constrained theory for TI sensitivity to kHz electric field given the attenuation by membrane low-pass filtering property, and for TI selectivity to deep structures given the distribution of modulated and unmodulated electric fields in brain. MethodsThe electric field threshold to modulate carbachol-induced gamma oscillations in rat hippocampal slices was determined for unmodulated 0.05–2 kHz sine waveforms, and 5 Hz amplitude-modulated waveforms with 0.1–2 kHz carrier frequencies. The neuronal effects are replicated with a computational network model to explore the underlying mechanisms, and then coupled to a validated current-flow model of the human head. ResultsAmplitude-modulated electric fields are stronger in deep brain regions, while unmodulated electric fields are maximal at the cortical regions. Both experiment and model confirmed the hypothesis that spatial selectivity of temporal interference stimulation depends on the phasic modulation of neural oscillations only in deep brain regions. Adaptation mechanism (e.g. GABAb) enhanced sensitivity to amplitude modulated waveform in contrast to unmodulated kHz and produced selectivity in modulating gamma oscillation (i.e. Higher gamma modulation in amplitude modulated vs unmodulated kHz stimulation). Selection of carrier frequency strongly affected sensitivity to amplitude modulation stimulation. Amplitude modulated stimulation with 100 Hz carrier frequency required ∼5 V/m (corresponding to ∼13 mA at the scalp surface), whereas, 1 kHz carrier frequency ∼60 V/m (∼160 mA) and 2 kHz carrier frequency ∼80 V/m (∼220 mA) to significantly modulate gamma oscillation. Sensitivity is increased (scalp current required decreased) for theoretical neuronal membranes with faster time constants. ConclusionThe TI sensitivity (current required at the scalp) depends on the neuronal membrane time-constant (e.g. axons) approaching the kHz carrier frequency. TI selectivity is governed by network adaption (e.g. GABAb) that is faster than the amplitude-modulation frequency. Thus, we show neuronal and network oscillations time-constants determine the scalp current required and the selectivity achievable with TI in humans.

High-Speed Optical Digital-to-Analog Converter Operation of Compact Two-Segment All-Silicon Mach–Zehnder Modulator

An optical digital-to-analog converter (DAC) is a promising solution for the efficient generation of multilevel modulation signals without a high-speed electrical DAC and a large swing linear driver. We report the design and characterization of an all-Si segmented Mach–Zehnder modulator for an optical DAC transmitter. The modulator comprises a forward-biased positive intrinsic negative (PIN) phase shifter integrated with a passive resistance and capacitance (RC) equalizer (PIN-RC) to optimize a tradeoff between modulation efficiency and analog bandwidth. We successfully confirmed an eye diagram of 90-Gbaud NRZ signal owing to a wide 3-dB bandwidth of 43.9 GHz. Additionally, a 70-Gbaud four-level pulse amplitude modulation (PAM4) waveform can be obtained via the optical DAC operation using a lumped segmented modulator because of its broad electro–optic bandwidth and uniform characteristics. A two-segmented modulator has a compact footprint of 300 μm × 600 μm. Error-free performances based on the patterns of the PRBS11 of NRZ signals were obtained at 50–70 Gbaud. The bit-error-rates of 60-Gbaud PAM4 and 70-Gbaud PAM4 were less than the 7% hard and 25.5% soft decision forward error correction limits, respectively. The optical DAC transmitter using an all-Si segmented PIN-RC modulator is suitable for next-generation high-speed multilevel transmitters.

Self-copy-shift-based differential phase extracting method for fiber distributed acoustic sensing

A differential phase extracting method based on self-copy-shift for distributed acoustic sensing is proposed. Heterodyne and optical hybrids are used to realize high signal-to-noise ratio in-phase and quadrature-phase (IQ) signal measurement. The measured signals are self-copied and shifted for certain data points, and then they are digitally mixed with the original signals to construct the differential phase. The four produced signals are then combined to carry out IQ demodulation. An experiment with strain having an amplitude modulation waveform is carried out. The results showed that waveform information can be recovered well, and the signal-to-noise ratio achieves 32.8 dB.

Dynamic Phase Demodulation Algorithm for Phase-Sensitive OTDR With Direct Detection

A dynamic phase demodulation algorithm for direct detection $\Phi $ -OTDR is proposed and experimentally demonstrated. It offers a way for single channel direct detection $\Phi $ -OTDR, which is the simplest and most cost-effective structure, to realize phase demodulation. Through making use of the redundant information between the sensing series from the vibration impacted region, the local extreme points(LEP) of the sensing series can be divided into two types. The second type LEP offers light phase quadrant information, and then the phase can be further reconstructed through anti-trigonometric function. Single frequency and amplitude-modulated waveforms have been correctly demodulated. The demodulated phase amplitude agrees well with theoretical value, which shows a potential application in strain measurement.

Arbitrary Waveform Generators Using Current-Controlled Current Conveyor Transconductance Amplifier and Current Conveyor Analog Switches

This paper presents a new amplitude modulation (AM), frequency modulation (FM), amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) and quadrature amplitude modulation (QAM) waveform generators using current current-controlled conveyor transconductance amplifier (CCCTA) and current conveyor analog switches (CCASs). The CCCTA around with capacitors and resistors are used to generate high-frequency carrier which is worked as a quadrature oscillator. The oscillating frequency of oscillator can be controlled using the bias current of CCCTA, therefore FM and FSK waveforms can be obtained by applying information signal through the bias current of CCCTA. Unlike previous waveform generators, proposed circuit uses second generation current conveyor (CCII) to work as CCAS and AM, ASK, PSK and QAM waveforms can be obtained by putting information signals to control switches that realized using CCIIs. The proposed circuit has been simulated using 0.18[Formula: see text][Formula: see text]m CMOS [Formula: see text]-well process from TSMC. The simulation results are used to confirm workability of the proposed circuit.

Two-photon frequency division multiplexing for functional in vivo imaging: a feasibility study.

Recently, we presented a new approach to create high-speed amplitude modulation of femtosecond laser pulses and tag multiple excitation beams with specific modulation frequencies. In this work, we discuss the utility of this method to record calcium signals in brain tissue with two-photon frequency-division multiplexing (2P-FDM) microscopy. While frequency-multiplexed imaging appears slightly inferior in terms of image quality as compared to conventional two-photon laser scanning microscopy due to shot noise-induced cross-talk between frequency channels, applying this technique to record average signals from regions of interest (ROI) such as neuronal cell bodies was found to be promising. We use phase information associated with each pixel or waveform within a selected ROI to phase-align and recombine the signals into one extended amplitude-modulated waveform. This procedure narrows the frequency detection window, effectively decreasing noise contributions from other frequency channels. Using theoretical analysis, numerical simulations, and in vitro imaging, we demonstrate a reduction of cross-talk by more than an order of magnitude and predict the usefulness of 2P-FDM for functional studies of brain activity.

Digital Signal Detection by a Glow Discharge Detector

A glow discharge detector (GDD) is a plasma neon bulb originally designed for lighting. However, it was demonstrated that it can be used for the detection of electromagnetic radiation in a wide range of frequencies up to millimeter and submillimeter waves. It is shown here that the device can be used not only as a detector but also as a heterodyning mixer. Experimental measurements confirm an analytical derivation, demonstrating that quadrature modulated signals can be downconverted to an intermediate frequency (IF) without distortions, even if the amplitude and phase are modulated simultaneously, as in quadrature amplitude modulation (QAM) waveforms. Digital QAM waves at the microwave frequencies were directly illuminated onto the GDD and mixed with radiation produced by a local oscillator. The resulted GDD current was analyzed to verify that the product maintains its QAM constellation also at the IF. The GDD detects both the magnitude as well as the phase in a manner that allows the complete demodulation of the digital data using several modulation methods. The experimental setup, as well as the results, is presented. It is concluded that the GDD can be employed also as a direct mixer in a digital receiver chain. The notation “GDM” is proposed for it which stands for “glow discharge mixer.”

Effect of jammer signal on stepped frequency PAM4 radar waveforms

In a RADAR system, the introduction of a jamming signal in the received signal path makes the distinguishing of targets a challenging task. The most frequently used signals in radar are of the continuous and pulsed wave types. When using pulsed radar signals, modification of the waveform is required in the radar operations for improved target sensitivity and range resolution. In addition, for the monostatic radar case, two antennas are used, one each at the transmitter and receiver sides. In the work discussed here, along with the monostatic model radar signals such as the stepped frequency waveform (SFW) and the 4-level pulse amplitude modulation (PAM4) waveform are considered, and they are observed to be powerful modulation techniques capable of avoiding jamming. SFW is used to obtain high range resolution, while PAM4 is used to obtain lower bandwidth. Combination of SFW and PAM4 provides a compound pulsed radar modulation technique which shows efficient results in target detection. To examine the performance of SFW and PAM4, simulation is done using a monostatic radar model under different conditions such as multipath propagation, fading and jamming. The compound pulsed radar modulation techniques are shown as being able to detect targets in the presence of a jamming signal. The results are analyzed in terms of the critical radar parameters such as range-speed response, burn-through range, cross-over range and signal-jammer noise ratio.

Arbitrary waveform modulated pulse EPR at 200 GHz

We report here on the implementation of arbitrary waveform generation (AWG) capabilities at ∼200GHz into an Electron Paramagnetic Resonance (EPR) and Dynamic Nuclear Polarization (DNP) instrument platform operating at 7T. This is achieved with the integration of a 1GHz, 2 channel, digital to analog converter (DAC) board that enables the generation of coherent arbitrary waveforms at Ku-band frequencies with 1ns resolution into an existing architecture of a solid state amplifier multiplier chain (AMC). This allows for the generation of arbitrary phase- and amplitude-modulated waveforms at 200GHz with >150mW power. We find that the non-linearity of the AMC poses significant difficulties in generating amplitude-modulated pulses at 200GHz. We demonstrate that in the power-limited regime of ω1<1MHz phase-modulated pulses were sufficient to achieve significant improvements in broadband (>10MHz) spin manipulation in incoherent (inversion), as well as coherent (echo formation) experiments. Highlights include the improvement by one order of magnitude in inversion bandwidth compared to that of conventional rectangular pulses, as well as a factor of two in improvement in the refocused echo intensity at 200GHz.

Single-mode instability in standing-wave lasers: The quantum cascade laser as a self-pumped parametric oscillator

We report the observation of a clear single-mode instability threshold in continuous-wave Fabry-Perot quantum cascade lasers (QCLs). The instability is characterized by the appearance of sidebands separated by tens of free spectral ranges (FSR) from the first lasing mode, at a pump current not much higher than the lasing threshold. As the current is increased, higher-order sidebands appear that preserve the initial spacing, and the spectra are suggestive of harmonically phase-locked waveforms. We present a theory of the instability that applies to all homogeneously broadened standing-wave lasers. The low instability threshold and the large sideband spacing can be explained by the combination of an unclamped, incoherent Lorentzian gain due to the population grating, and a coherent parametric gain caused by temporal population pulsations that changes the spectral gain line shape. The parametric term suppresses the gain of sidebands whose separation is much smaller than the reciprocal gain recovery time, while enhancing the gain of more distant sidebands. The large gain recovery frequency of the QCL compared to the FSR is essential to observe this parametric effect, which is responsible for the multiple-FSR sideband separation. We predict that by tuning the strength of the incoherent gain contribution, for example by engineering the modal overlap factors and the carrier diffusion, both amplitude-modulated (AM) or frequency-modulated emission can be achieved from QCLs. We provide initial evidence of an AM waveform emitted by a QCL with highly asymmetric facet reflectivities, thereby opening a promising route to ultrashort pulse generation in the mid-infrared. Together, the experiments and theory clarify a deep connection between parametric oscillation in optically pumped microresonators and the single-mode instability of lasers, tying together literature from the last 60 years.